1. Field of the Invention
This invention relates to a coating composition for forming a protective film of a colored rubber portion of a tire and a protective film produced thereby, and more specifically to a coating composition for forming a protective film of a colored rubber portion having a different color(almost white) from a base color(black) of a sidewall portion of a tire and a protective film formed thereby.
2. Prior Art
Conventionally, on a sidewall of a tire, there have been sometimes arranged ornaments made of white rubber and the like in order to add beauty to a tire, along a sidewall portion of a tire, such as a circular line or letters representing a tire manufacturing company. Such tires are so-called white-line tires, white-letter tires, etc. When transporting or storing such tires in a pile, however, there often occur such problems that a colored rubber portion of a tire is contaminated or discolored due to antioxidants, process oil and the like bleeding from adjoining tires, also due to dust and refuse attached with adjoining tires, and that a colored rubber portion of a tire is likely to be damaged due to the contact of tires with each other.
In order to solve the above problems, the following measures have been taken:
1) wrapping a whole tire with synthetic papers and the like;
2) applying a soft plastic film to the colored rubber portion; and
3) coating a colored rubber portion with water-soluble paint, e.g., blue-colored paint, to form a thin film.
Wrapping a tire as in measure 1) is time-consuming and synthetic papers used for wrapping yield industrial wastes. In the case of the above measure 2), adhesives coated to a soft plastic film increase its viscosity at a low temperature, and as a result the peel strength also becomes greater. Accordingly, peeling operation was not easily conducted before using such a tire. Even if peeling operation is done at a room temperature or comparatively high temperature, adhesives tend to remain on the surface of the colored rubber portion after completion of film peeling, which spoils the beauty of tires. Peeled films should also be disposed as industrial wastes.
According to the above measure 3), it is necessary to remove a thin film of colored water-soluble paint from a colored rubber portion using water or the like before using a tire, so that a colored rubber portion on the sidewall is maintained with its beauty. However, such washing operation is time-consuming and a thinner film is required for easy removability. A thinner film, however can not enhance properties of preventing contamination and damages of a colored rubber portion.
It is therefore an object of the present invention to provide a coating composition for forming a protective film of a colored rubber portion of a tire sidewall to maintain a color at a colored portion with its beauty and a protective film produced thereby wherein the above-described contamination and damages can be fully prevented without troublesome operation such au peeling and removing a film or disposing industrial wastes.
The inventor has made various investigations for attaining the above mentioned objects and as a result, it has been found out that a film made of specific resins which are soluble by water or lower alcohol is colorless and transparent and has satisfactory tenacity required for a protective film and is easy to handle since water and lower alcohol can be used as a solvent.
Thus, the present invention provides, as claimed in claim 1, a coating composition for forming a protective film of a colored rubber portion of a tire comprising at least one resin with polymerization degree 200 and above selected from the group consisting of polyvinyl acetate resin, vinyl acetate-acrylic acid copolymer resin, vinyl acetate-methacrylic acid copolymer resin, vinyl acetate-alkane acid copolymer resin, vinyl acetate-itaconic acid copolymer resin, vinyl acetate-crotontc acid copolymer resin, vinyl acetate-fumaric acid copolymer resin, vinyl acetate-maleic acid copolymer resin, vinyl acetate-maleic anhydride copolymer resin and polyvinyl alcohol, and at least one solvent for dissolving resins selected from the group consisting of lower alcohols and water, wherein a solution obtained having 30 cps-1,000 cps viscosity.
Any lower alcohol which is liquid at a room temperature is applicable to the present, invention. Methanol, ethanol, propyl alcohol, isopropyl alcohol, butyl alcohol, isobutyl alcohol are preferable, and particularly methanol and ethanol are more preferable. Water and lower alcohols are applicable separately or in a mixed form of water and at least one of lower alcohols or in a mixed form of at least two lower alcohols. Preferable solvents nay be selected in consideration of solubility of resins and a solution viscosity.
Taking into account of a drying speed after coating, it is preferable to use lower alcohol with lower boiling temperature separately. e.g., methanol or ethanol. Solvent having a higher boiling temperature such as water may be mixed with lower alcohols having a lower boiling temperature.
Polyvinyl acetate resin, vinyl acetate-acrylic acid copolymer resin, vinyl acetate-methacrylic acid copolymer resin, vinyl acetate-alkane acid copolymer resin, vinyl acetate-itaconic acid copolymer resin, vinyl acetate-crotonic acid copolymer resin, vinyl acetate-fumaric acid copolymer resin, vinyl acetate-maleic acid copolymer resin, vinyl acetate-maleic anhydride copolymer resin, and polyvinyl alcohol can be applied separately or in a mixed form of at least two thereof. The polymerization degree shall be not less than 200. When the polymerization degree of a resin is less than 200, the tenacity of a formed protective film is not satisfactory and a protective film is inferior in durability and stability, thus resulting in rupture of the protective film during transporting or storing of tires. Then properties of preventing contamination and damages of a colored rubber portion are injured.
The viscosity of solution including one or two resins dissolved in the solvent shall be 30 cps-1,000 cps by measurement at 25xc2x0 C. using a SB type viscometer in accordance with a rotational viscometer method described in the Japanese Industrial Standardxe2x80x94JIS K 5400 (hereinafter same measuring method is applied to measure solution viscosity). When the solution viscosity is less than 30 cps, a protective film obtained can not fully perform such functions as preventing contamination and damages. On the other hand, when the solution viscosity is more than 1,000 cps, uniform coating of the protective film is difficult. Preferable solution viscosity is 200 cps-600 cps.
A coating composition obtained has the following characteristics: 1) each resin component is easily dissolved into the above mentioned solvent or mixed solvent and a coating composition is easily manufactured; 2) coating operation onto a colored rubber portion is easily conducted by means of spray coating or brushing; 3) water or lower alcohol is used as solvent, so that easy and fast drying is performed after coating and rubber components of a tire are not damaged by a coating composition and besides no environmental pollution occurs; and 4) a protective film formed with such composition is colorless and transparent and has preferable tenacity.
The present invention also provides, as claimed in claim 2, a protective film formed on the colored rubber portion of a tire using the above coating composition claimed in claim 1. A protective film thus obtained is colorless and transparent and has superior tenacity, so that the function of a protective film such as preventing contamination and damages can be fully performed while maintaining a colored rubber portion with its beauty. As a result, the protective film according to the present invention requires no troublesome operations such as wrapping a tire and removing a wrap, applying and peeling a plastic film or removing a thin film of colored water-soluble paint as described in connection with the prior arts. Furthermore, there yields no wastes to be disposed.
The thickness of a protective film is preferably 15 xcexcm-100 xcexcm, as claimed in claim 3. When the thickness is less than 15 xcexcm, the effect of preventing contamination and damages is inferior. On the other hand, when the thickness is more than 100 xcexcm, there tends to occur cracks on a protective film. Thickness of a protective film is preferably 20 xcexcm-70 xcexcm.
The present invention is now explained with the following embodiments.
Embodiment 1
One of preferable coating compositions for forming a protective film of a colored rubber portion of a tire was obtained by dissolving polyvinyl acetate resin or any one of aforementioned vinyl acetate copolymer resins having a polymerization degree 200-5000 into a mixed solvent comprising methanol, ethanol and water with the solution viscosity of 200 cps-600 cps.
The coating composition obtained was coated by means of spray coating on a white circle line on a side wall portion of a tire By natural drying, a colorless and transparent protective film of high tenacity was obtained with the thickness of 20 xcexcm-70 xcexcm.
Embodiment 2
Another preferable coating compositions for forming a protective film of a colored rubber portion of a tire was obtained by dissolving polyvinyl alcohol having a polymerization degree 200-5000 into water with the solution viscosity of 200 cps-600 cps.
The coating composition obtained was coated by means of brushing on a white circle line on a tire side wall portion. By natural drying, a colorless and transparent protective film of high tenacity was obtained with the thickness of 20 xcexcm-70 xcexcm.
Both in the above embodiments, easy coating and easy and speedy drying are performed. The protective film obtained was colorless and transparent and of high tenacity, so that contamination or damages of a white circle line on a sidewall portion caused by contact with adjoining tires when transporting or storing was fully prevented, while keeping the white circle line with its beauty.